Antiroll facilities

ABSTRACT

A weighted rod and a coacting contact carrier frictionally entrainable by a mounting on a rolling craft generate timing signals in positions of maximum lateral excursions of craft with reference to a longitudinal axis, the rod being pivotally mounted aboard the craft on a shaft parallel to that axis so as substantially to maintain a vertical amplitude, position whereby two sets of contacts on these relatively movable members are alternately closed during respective amplitude. of the rolling motion. The timing signals control the operation of an antiroll system, specifically two stabilizer tanks on opposite sides of the craft which are alternately filled with and drained of water and which are supplemented by a further pair of tanks whose relative water volume is altered to balance deviations of the mean attitude of the craft from an upright position as likewise determined from these timing signals.

United States Patent [72] Inventors Albert Viollet Bagneux; EdmondVoillaume; Francois Bouilhol, Paris, France [21 Appl. No 787,871 [22]Filed Dec. 30, 1968 [45] Patented Feb. 2, I971 [73] Assignee AssociationDes Ouvriers En Instruments de Precision Paris, France v a French bodycorporate [32] Priority Dec. 29, 1967 [33] France [31] 134315 [54]ANTIROLL FACILITIES 13 Claims, 20 Drawing Figs.

[52] US. Cl 114/125 [51] Int. Cl 1163b 43/06 [50] Field ot'Search114/122, 125, 126; ZOO/61.48

[56] '..eierences Cited UNITED STATES PATENTS 2,338,147 1/1944 Steinen114/122 Prior Art 2,618,712 11/1952 Moledzky ..200/61.48(UX) 3,265,0298/1966 Laurenti 114/122 Primary Examiner-Trygve M. Blix Attorney-Karl F.Ross ABSTRACT: A weighted rod and a coacting contact carrierfrictionally entrainable by a mounting on a rolling craft generatetiming signals in positions of maximum lateral excursions of craft withreference to a longitudinal axis, the rod being pivotally mounted'aboardthe craft on a shaft parallel to that axis so as substantially tomaintain a vertical reference position whereby two sets of contacts onthese relatively movable members are alternately closed duringrespective half-cycles of the rolling motion. The timing signals controlthe operation of an antiroll system, specifically two stabilizer tankson opposite sides of the craft which are alternately filled with anddrained of water and which are supplemented by a further pair of tankswhose relative water volume is altered to balance deviations of the meanattitude of the craft from an upright position as likewise determinedfrom these timing signals.

' PATENTEUFEB 21971 SHEET 1 0F 7 Albert Viola! Invemors.

By g iR Edmond voillaume Francois Bouilhol vllllllll AttorneyPATENTEDFEQ 21 man 3,559,610

u Alberf Viola? Edmond voillaume Francois Bouilhol Inventors.

9 Ka Tm 4 Attorney PATENIEUFEB 2m: 3559 55 .snmunw I OObOE' lilil IAlbert violel Edmond Voi/Iaume Francois Bouilho:

Inventors.

89 Karl .Attome PATENTEDIFEB 2L9?! SHEET 7 3.559610 Albert viollef a,mm. uls 5w w Qwmm m V e m bV nwm n 0 mm, mm Er PATEINTEDI'FEBI 2:971' Vsum 7 or 7- 3'559'610 Alberf Viol/sf Edmond Voilla e Francois BowInvenfors.

ANTIROLL FACILITIES Antiroll devices comprise means which producetorques opposing the roll of seagoing ships and other craft and whichare controlled so that the stabilizing action anticipates the rollmovement. Accordingly, the control is usually effected by appropriatemeans responsive to the angle of tilt of the ship, the rate of change ofsuch angle and possibly the acceleration of the variation and thedifferential thereof. The counter-torqueproducing means can bedynamici.e., act in accordance with the ships speed of travel-and insuch cases are usually ailerons which project from either side of thecraft. The ailerons can be permanently extended in rough weather andadjusted by variation of their inclination or pitch angle, or they canhave a fixed orientation but be retracted or extended to a variabledegree; ailerons are also known whose effective length and orientationare fixed but which are brought out for varying periods of time.

Such stabilizing means can also be static, i.e. based on the weight ofshiftable masses. It has already been suggested that moving masses ofliquid be used for this purpose, to which end vessels are disposed alongthe edges of the ship symmetrically with reference to its axis; a massof water is then transferred from a vessel or tank on one edge to a tankon the other edge at appropriate times. The disadvantage of thissolution is that the water-transfer operations require very largeenergies. To obviate this disadvantage, it has been suggested that thetanks be disposed below the water line and that external water heallowed to enter the tanks and be expelled therefrom in the rhythm ofthe rolling notions to be counteracted. This measure avoids theexpenditure of energy for the transfer of water from one side of theship to the other; the tanks can be filled just by hydrostatic pressurewith an increase of delivery if the filling orifices are appropriatelyoriented, and the power required is merely that necessary for emptyingthe tanks with the aid of compressed air. Such stabilizers have aconsiderably larger time constant than systems operating with extendableand/or orientable ailerons or fins.

Rolling can be considered a combination of two phenomena resulting in acomposite oscillatory motion: a natural oscillation of the craft aboutits longitudinal axis, with a periodicity which is fairly constantalthough dependent upon the loading of the ship and the swell of thesea, and a forced oscillation caused solely by the swell andsuperimposed upon the natural oscillation of the ship with, usually, amuch longer periodicity. Theoretical studies of these movements showthat an antiroll device can be controlled in response to data relatingto oscillations immediately preceding the oscillations to be damped,such as the times of occurrence of the peaks, the length of ahalf-period, the roll amplitude and the mean position of the ship.

The general object of our present invention is to provide means forobtaining some or all of these various data and using them to controlantiroll stabilizers. More particularly, our invention aims at providingmeans for forecasting the rolling movement to be stabilized from themotion, during the immediately preceding complete roll cycle, of avertical reference standard aboard the craft.

In its broader aspects, our invention provides a reference member ofsubstantially fixed absolute orientation maintained by gravity orinertia, a cooperating member mounted on the craft for lateral angularentrainment, and coacting circuit means on these members for actuating astabilizer-control system in timed relationship with therelativemovement of the members.

According to a more specific feature of our invention, a rocking memberor plummet swivelable around at least one longitudinal axis relativelyto the ship while maintaining a substantially vertical position isassociated with a balanced unit movable around an axis coincident withthe swivel axis of the rocking member, this unit bracketing the rockingmember with play and comprising on each side thereof a contact memberoperated by the interengagement of the rocking member and the mobileunit. In a device of this kind, there occurs at each peak of atransverse oscillatory movement of the ship a switchover of contactscarried by the coacting elements so that a control signal is generatedto indicate the time of occurrence of such peak.

Preferably, such a rocking member supports at least one slider movablealong a track of a DC -energized potentiometer connected with the ship,the voltage thus taken from the potentiometer in certain positions beingstored to furnish an analogue output representing one of the parametersof the oscillating movement. Consequently, a comparison of the extremevoltages obtained in the rocking movement enables their mean value to beascertained, as a measure of the mean attitude or angle of heel of theship, as well as their difference which is a function of roll amplitude.

According to another feature of the invention, roll compensation isproduced by two independent torque generators respectively responsive tothe natural roll of the ship and to the oscillation superimposedthereupon, only the torque generator counteracting the natural roll ofthe ship being controlled in dependence upon roll amplitude whereas theother torque generator is controlled only in dependence upon the meanposition of the ship between two consecutive opposite peaks of theoscillation. This technique assumes, with good approximation of reality,that the lower-frequency oscillation superimposed upon the natural rollof the ship is a determining factor only for the mean position of thecraft around which the oscillations occur, but that the amplitude of thecomposite motion in practice depends only upon the natural oscillationof the ship about its longitudinal axis.

Although the principles explained above have general applicability, weshall particularly describe hereinafter their utilization with antirolltorque generators of the two types referred to above.

In the accompanying drawing:

FIG. I is a diagrammatic plan view of antiroll damping equipmentcomprising tanks communicating with a body of liquid surrounding acraft;

FIG. 2 is a cross section on the line II-II of FIG. 1;

FIG. 3 is a cross section on the line III-III of FIG. 2;

FIG. 4 is a view in diagrammatic cross section of a ship havingaileron-type antiroll equipment;

FIG. 5 is a side view on the line V-V of FIG. 4;

FIG. 6 is a diagram showing the operating conditions of a tank-typestabilizer as illustrated in FIGS. 1-3;

FIG. 7 is a block-schematic view of a system for controlling a tank-typestabilizer of the kind shown in FIGS. 1-3;

FIG. 8 is a partly diagrammatic side elevation of a device for providinga vertical reference standard and of associated electrical circuitry;

FIG. 9 is a side view on the line IX-IX of FIG. 8;

FIG. 10 is a diagrammatic view of the device shown in FIGS. 8 and 9,along with its electrical circuit connections;

FIG. 11 shows a circuit diagram for evaluating the data obtained fromthe assembly of FIGS. 8-10;

FIG. 12 is a graph showing variations in the operating time of a torquecompensator plotted against the amplitude of the roll to be compensated;

FIG. 13 is a circuit diagram, more detailed than FIG. 7, of a controlsystem for a tank-type stabilizer as a shown in FIGS. 1-

FIG. 14 is a diagram showing how the system of FIG. 13 operates independence upon the real amplitude of the roll to be corrected;

FIG. 15 is a diagram of an installation for correcting the mean angle ofheel of a ship;

FIG. 16 is a diagram of a balanced amplifier for the circuit of FIG. 11;

FIG. 17 is a simplified alternative form of circuit diagram forproviding a control signal after a quarter-period of the natural roll;

FIG. 18 is a diagram serving to explain the operation of the systemshown in FIG. 17; and

FIGS. 19 and 20 are diagrams serving to explain the use of aileron-typetorque correctors for counteracting rolling motion.

FIGS. 1-5 show conventional antiroll devices 111 which the invention maybe of use.

A ship 1 shown in FIGS. 1-3 has tanks 2,, and 2, disposed along its portand starboard sides, the subscripts B and T standing for the Frenchdesignations babord (port) and tribord (starboard). Each tank is formedwith two orifices 3, 4, the orifice 3 being open toward the front andthe orifice 4 being open toward the rear of the craft. Since all theseorifices are disposed below sea level 5, the tanks can be filled throughthe orifices 3 by both hydrostatic and dynamic pressure; when the shipis moving, emptying of the tanks is assisted by the dynamic negativepressure produced in the rear of the orifices The tanks can be filled byventing their interior to atmosphere via conduits 6 and valves 7. Thetanks are emptied by means of compressed air supplied from a reservoir 8by a pump 9; valves 10, ll, controllable by suitable servomechanisms,also intervene in the filling and draining of the tanks.

In the construction shown in FIG. 1, the ship has two pairs of tanks,which can be operated simultaneously, on each side. As shownhereinafter, each individual tank of these identical pairs mayadvantageously be controlled independently.

In the antiroll installation shown in FIGS. 4 and 5, actuators 12 canextend ailerons or fins 13 of hydrofoil profile from opposite sides ofthe craft; with proper angular orientation, these fins can provideuplift or downthrust compensating for the rolling motion and varying asa function of the forward speed of the craft. The pitch of these finsand/or their effective length L, i.e. the degree of their projectionfrom the sides of the craft, may be controlled by conventional means.

Systems using stabilizing masses, such as the tank-type stabilizer shownby way of example in FIGS. 1-3, are operative whether the ship isstationary or moving (being more effective when the ship is in motionthan when it is not), but ailerontype stabilizers are operative onlywhen the ship is moving.

In the ensuing description of FIGS. 7-16 we shall, for convenience,limit ourselves to a discussion of tank-type antiroll stabilizers of thekind shown in FIGS. 1-3 whose damping effect depends upon the state oftank filling, thus upon a continuously varying quantity, so that anappreciable time factor intervenes in the antiroll action, incontradistinction to the almost instantaneous compensating effect offin-type stabilizers.

It will be assumed that the filling and emptying of the tanks proceedsat a constant rate and that the lever arm of the tanks relative to thelongitudinal axis of the ship is the same for all angles of roll up to alimiting value of approximately 15. The stabilizing torque developed byeach tank can therefore be represented by a sequence of linear functionsof time.

In the case of a simple roll the compensating action provided by thetanks can be represented in the manner shown in FIG. 6, where the timeaxis r represents the mean vertical position of the ship and the rollangles 0 on either'side of this mean vertical position are plotted alongthe ordinates, up for one side (e.g. port) and down for the other. Asinusoidal line 14 can therefore represent the simple or natural rollhaving, as an undamped oscillation, a natural period T,,. To damp thisassumedly large oscillation when the angle of heel on either side is amaximum, i.e. when the bridge has its greatest list toward such side(e.g. to port as shown at time t 0 in FIG. 6) and the ship starts tostraighten, the corresponding side (here the port side) of the ship mustbe weighted to limit the restoring or straightening torque and thus toattenuate the oscillation. On the other hand, when the ship passesthrough its normal position before tilting to the other side at anangular velocity which is then at its maximum, it must be lightened toreduce the mass actually performing the oscillating movement. To achievemaximum damping, therefore, the tanks must be filled when the shipreaches its greatest angle of heel, whereupon the rising tanks justfilled should be drained as soon as the mean position is reached.

Consequently, as FIG. 6 shows, the tanks on each side can startreceiving liquid at the time when the angle of heel to such side is amaximum lateral excursion. Since the filling rate is consideredconstant, a straight line 15, can represent filling. The voiding of thesame tank can start at a time t near the point T,,/4 corresponding tothe passage of the sinusoidal line 14 through zero, with a straight line16, representing drainage.

The volume of water used in this case for stabilization corresponds tothe triangle bounded by the abscissas I and the straight lines 15,, 16,which represent the stabilizing torque on a convenient scale.

However, this correction may sometimes be excessive and, if the roll isof low amplitude, may make the ship oscillate. In this case therefilling must start at an instant, such as t,, after the time ofmaximum angle of heel, with'voidance still commencing at a time t nearT,,/4. The roll compensation provided on each side then corresponds tothe hatched triangles whose sides 15,, 16 are parallel to themaximum-correction sides 15,, 16,.

FIG. 12 illustrates this variation of damping in graph fonn.

As already stated, the tanks have more effect when the ship is movingthan whenit is not. If the start of tank filling at maximum tilt oneither side produces a damping a,, when the ship is stationary and B,when the ship is moving (the angle a, being being 2' and the angle [3,,being 3" by way of example), the damping factor AM is zero when theinstant t, of incipient refill, occurring at time 116/4, coincides withthe instant t of incipient voiding. It will be assumed, in closeapproximation to the actual facts, that a shift of the time t, betweenthe antinodal and nodal points 0 and T,,/4 causes a variation of thedamping factor AM as represented by the straight line D,.. This linearvariation of damping in dependence upon t, (delay in the start offilling relative to peak time 0) is significant for the interpretationof the graph of FIG. 14 discussed hereinafter.

As shown in FIG. 6, the periodically recurring corrective action of theantiroll system is out of phase with the oscillation 0 to becompensated, a factor which modifies the period of such oscillation. Thetrue oscillation period will be designated hereinafter by the referencecharacter T.

As already stated, however, rolling is a composite movement resultingfrom a combination of the natural roll of the ship sustained by externalforces, with a superposed sway produced by the swell.

According to a feature of our invention, this complex movement isconsidered as a simple oscillation whose mean line is not the axis I buta curve 17 (representing an oscillatory phenomenon of amplitude 0,determined graphically by the sequence of mean ship positions relativeto the horizontal (or the vertical) between two consecutive swings inopposite lateral directions. Full roll correction therefore comprises atany time a correction of the ship's side-to-side movement and acorrection of the ships mean position, i.e. a rebalancing relative toits longitudinal axis, so as to oppose the slow movements tending totilt the ship to one side or the other. This latter correction can beachieved by varying the state of filling of a pair of balancing tanks(28,, 2T in FIG. 7) under the control of a signal representing the meanattitude of the ship between two extreme positions on opposite sides.

We shall describe hereinafter how such a signal can be generated.

Correction of side-to-side movement of the ship depends for each sideupon a determination of the instants t, and t, which are in turndependent upon the times t 0 when the roll reaches its maximum excursionalternately on each side, upon the half-amplitude 0,, of the roll whichdetermines the required degree of damping and therefore the delaybetween the instants t, and antinodal points 0, and upon the mean tiltangle 7 0,, of the ship compared with its actual list 0 to determine thetime t,, thus obviating the need for direct determination of theduration of each quarter-period after passage through the peak.

The installation can be realized as schematically shown in FIG. 7.

Associated with a vertical reference standard VR articulated around apivotal axis parallel to the ship's longitudinal axis is anelectromechanical unit MI which signals the instants t marking theantinodal points for port and starboard, along with signals 0,, 0,, and0,, 6,, and 0, which are passed to two controllers CaB (for port) andC,,T (for starboard) sharing a common section CV. From these data thecontrollers determine the starting times t,.(B) and t,(T) for thefilling of the corresponding tanks 28, and 21, by the energization ofthe respective electromagnetic valves EB and ET, while the commoncontrol circuit CV determines the starting time t, for the subsequentemptying by breaking the valve-energizing circuit so that the compressedair can expel the water from the tanks.

The signal 0 an analogue of the mean angle of the ship relative to thevertical, also goes to a regulator AS receiving feedback infonnation onthe liquid levels in the tanks 28, and 2T whose state of filling iscontrolled by this regulator through respective electromagnetic valvesF8 and F1.

When the ship is balanced and there is no angle of heel, the two maintanks 2B,, 2T, are full. The maximum restoring torque in either sense isof course produced by emptying a single main tank, i.e. the one on theside where weighthas to be reduced. A similar variation restoring torquecan be produced either by emptying some liquid from one of the twosupplemental tanks 2B,, 2T or by introducing an equivalent quantity ofliquid into the other supplemental tank.

FIG. shows a circuit arrangement for the regulator AS. A voltage e whichis an analogue of 0,, (obtained in a manner described hereinafter), iszero when the mean position of the ship is horizontal, positive for amean angle of heel to one side, and negative for an opposite mean tilt;this voltage is fed to two windings 81 n and 81 of two polarized relayswhose arma tures 82B, 82T control via intermediate relays (not shown)the electromagnetic valves FE and FT, respectively; the two armaturescould also be replaced by a single contact arm.

At their other ends the windings 81 81, are supplied with voltagestapped from respective potentiometers 83,, 83 by sliders 85,, 85 underthe control of level-indicating floats 84,, 84,4 in tanks 28,, 2Trespectively.

The reference voltage is therefore zero for both tanks when the same arefull; the potentiometer 83,, delivers a positive voltage which increasesin proportion to the drainage of tank 28,, whereas potentiometer 83under the same condition delivers an increasing negative voltage.Consequently, if the mean angle of heel is e.g. to starboard (enegative), tank 2T continues to drain as long as the absolute value of eexceeds that of the voltage on the slider 85,, but fills in the oppositecase.

FlGS. 8-11 show the assembly VR Ml, i.e. the means for obtaining thedata t,,, 0,, 0,, and 0.

The vertical reference direction can be provided by a gyroscope or moresimply by a pendulum or plummet 18 oscillating around a shaft 19 withnegligible friction, shaft 19 being borne by the ship and extendingparallel to the longitudinal axis thereof. To compensate for pitching,the shaft 19 can be mounted in a collar 19' journaled on a shaft 19"extending transversely of the ship. Mounted coaxially with shaft 19 is amobile unit 20 rotatable with low friction in a bearing 21 rigidlysecured to the mounting 112 for the shaft 19" and centered on thepivotal axis of pendulum 18; the unit 20 is oscillations of the craft,ferrule abuts either of the points 21,, 21, and remains in contacttherewith to its position of maximum tilt. On the other hand, as soon asthe return swing starts, the ferrule 23 withdraws from the engagedcontact and abuts the other one. Consequently, upon each reversal onecontact opens, with closure of the other contact after a time intervalwhich can be adjusted by means of the screw 22.

Thus, the times t, of maximum port and starboard tilt can be determinedby means of the set of contacts 23, 21,, 21,.

As FIG. 10 shows, the potentiometer tracks 30, 31 furnish analoguevoltages for the values of 0,, Le. the half-amplitude of the lateraloscillation of the ship, and of 9 i.e. the position balanced around itsaxis and is provided, on opposite sides of the pendulum rod 18, withcontact points 21,, 21, whose spacing can be adjusted by means of ascrew 22 spreading their resiliently biased supporting arms.

The contacts 21,, 21 are adapted to cooperate with a conductive ferrule23, mounted on the pendulum rod, energizable via a conductor 24connected to the shaft 19. The circuit is therefore closed externallyeither via a conductor 25, connected to contact 21, or via a cbnductor25 connected to contact 21,. Rod 18 also carries ferrules 26, 27 whichare connected to conductors 28, 29 and respectively slide alongpotentiometer tracks 30, 31 of resistance material rigid with frame 119.

With the friction of the mobile unit 20 in its bearing 21 slightlygreater than the pendulum friction, and with the weighted rod 18 stayingsubstantially vertical throughout the relative to the vertical of thebisector of the stroke angle 20,, measured during each oscillatoryperiod.

The ends of the arcuate tracks 30, 31 are respectively connected toground potential (0) and to a fixed operating potential A, the polarityof the voltage drop being opposite for the two tracks.

Let us assume that 18, and 18,, represent the two end positions of theplummet 18 and its sliders 26, 27 relative to the resistor strips 30,31. If a and a are the potentials of the contactors 26 and 27 in theposition 18,, and b and b' are the corresponding potentials in theposition 18,, the relationships a=A-a and b'=A-b exist between these twooutput voltages of generator 26 31 which are thus seen to be mutuallycomplementary. Consequently, if the magnitudes of a and of b are storedin the two limiting positions, the mean value e of the potentials willbe Thus, the voltage V0,,=e% is the analogue of the half-am- The meanposition 0,, can therefore be represented by an mean potential isanalogue voltage V 0, d corresponding to the input voltage e, of FIG.15.

FIG. 11 shows the basic design of the memory used to store maximum-swingpotentials and to deduce the mean of the data thus stored. Thepotentials, e. g. a and b, to be stored are transmitted via respectiveamplifiers Am to contacts k k from the corresponding slider 26 and/or 27of FIG. 10. The windings of relays K and K are connected, in circuits ofshort time constant (compared with period T or T to two normally chargedcapacitors G H and 6,. At the instants corresponding to maximum anglesof heel to port and starboard, respective contacts m m, are closed, in amanner described hereinafter, under the control of the contacts 21,, 21to complete respective discharge paths. The windings K K are thereforevery briefly energized at the appropriate time so that the short closureof their contacts k k alternately charges two identical capacitors H H,to the assigned potentials. The latter capacitors are seriallyinterconnected by a pair of equal resistances r,,.

If we neglect leakage losses of the two capacitors H and [-1,- aftertheir charging time, the mean d of their stored voltages appears at thejunction M of resistors r fand also yields the analogue voltage V6,, =ed supplied to the system AS of FIG. 15.

For rapid charging of the capacitors B II, and to make voltage eavailable throughout half an oscillation period, the amplifiers A shownin FIG. 11 may be of the balanced type as shown in FIG. 16. A voltage uof low value, which can be either positive or negative, is applied inparallel to two transistors 87, 88 which are similar to each other,except that transistor 87 is of the NPN type and transistor 88 is of thePNP type, and which are connected as emitter followers (with col lectorsat fixed potentials) by way of two resistors 89, 90 connected to zeropotential. One or the other of the transistors conducts according to thepolarity of the input voltage 14 is also present, without amplificationbut developed across a low impedance, at the common output terminal 91of the transistors.

Circuit arrangements similar to the one shown in FIG. 11 are also used,as described hereinafter, to produce the voltage e,,=V0,,. However,since these circuit arrangements are to establish a precise instantvoltage measurement, the connection between the two symmetricalresistances is not permanent but is completed only momentarily todetermine such instant (see FIG. 13); also, in order that the voltagescollected by the storage capacitors may be independent of previouscharges received thereby, the capacitors are periodically dischargedbefore being recharged to the new voltage to be stored. These circuitarrangements also use amplifiers A,,, for charging the storagecapacitors.

The voltage e, (which is alternately positive and negative) departsfurther from zero than does the voltage e As will become apparenthereinafter, the circuit arrangement Am operates satisfactorily as longas the ratio of its input and output voltages is linear at least for lowvalues of e,,, since in the case of higher voltages e,, i.e., largeoscillations of the ship the system operates continuously with maximumeffect and exact correspondence between input and output voltagesbecomes unimportant.

The circuit arrangement shown in FIG. 13 uses the basic systemshereinbefore described to obtain voltage analogues for 0, 0,, (for bothport and starboard), and for determining the times t,(B), t,(T) and t,.In FIG. 13 all relay contacts are shown in the unoperated position.Connected to contacts 2 1 and 21 are the windings of respective relaysM,,, M, which are therefore energized alternately, each substantiallyfor half an oscillation period between two maximum excursions, and arethen deenergized for the remainder of the cycle. Each of the theserelays comprises a reversing armature 35 35, and a circuit-closingarmature 36,,, 36 Each reversing armature, by changing over from itsback contact m, or m to its front contact m or m,,, enables thecapacitor G or G to charge through one of two like resistances r; forsubsequent discharge via the relay windings K and K respectively.

Each armature 36 36 completes, by way of a respective front contact m orm a circuit for supplying a negative energizing voltage to thecontrollers C,,B and C,,T. These circuits are closed by armatures D, andP of respective relays P, and P, which are alternately energized by areversing armature 37 of a polarized relay 39 in control circuit CV,this armature 37 moving toward one or the other of two bank contacts38,, 38 depending upon the direction of current flow through itswinding. The mode of energization of this winding will be describedlater.

The relays K, and K each comprise, in addition to their respectivearmatures k and k (see FIG. 11), two other armatures k k and k krespectively, through which the voltage a can be stored in respectivecapacitors C8,, CT and thevoltage b can be stored in respectivecapacitors CB CT The capacitors CB CB associated with the portcontroller caB cooperate with a pair of equal resistances r to form avoltage divider similar to the one shown in FIG. 11. However,

'the two resistors r instead of being permanently tied together, areintermittently interoonnectable by way of an armature m, of relay Mcooperating with bank contacts 101 and leading to controller C B. Asimilar circuit arrangement is operative in the case of the capacitorsCT CT and an armature m of relay M engageable with bank contacts 102 andconnected to controller C T. Via the controllers C,,B and C,,T,therefore, a voltage V0 which is an analogue of the maximum oscillationamplitude can be transmitted to port and starboard, respectively.

Via circuit-breaking armatures P P and capacitors 103,,, 103 relays Pand P deliver an energizing pulse to the windings of relays N, and Nrespectively, which lock via respective holding annatures n,,, n,, tonormally charged capacitors 104,,, 104 The relays N, and N thereforeremain operated for a brief but definite time. Via armatures n,,, n andn n the relays N and N briefly connect the capacitors CB,, CT and CB CTto zero potential for discharging them.

In each controller C,,B and C,,T the input voltage V0,, goes to the baseof a current-amplifying transistor T in the case of the controller C,,Twhich is connected asan emitter follower in series with two loadresistances r,,, r, controlled by a selector'switch 40 whereby one ofthe two voltages appearing at bank contacts 40a and 40b can be fed to avoltage divider formed by two equal and series-connected resistances r,.Consequently, the voltage at the junction 43 of the two resistances r,is the mean of the voltage picked up by selector 40 and the voltage at apoint 41 representing one terminal of a capacitor C the other terminalthereof being at ground (positive) potential. The voltage at point 43 istransmitted to the base 44 of a transistor Tb whose state ofconductivity controls the solenoid valve ET (FIG. 7) which, aspreviously explained, vents tank 23, to atmosphere when energized by apulse at time t,(T). In order that transistor Tb should becomeconductive, the voltage on its base 44 must reach a threshold VE (FIG.14). Identical circuitry in controller C,,B generates an output pulse attime t,(B) to energize the solenoid valve EB of FIG. 7.

Capacitor C, is charged through an adjustable resistor r, by negativevoltage transmitted via contacts P 36 the latter closing shortly afterthe time of maximum excursion of the oscillation on the particular sidehere concerned.

From the time t,,(B) at which contact 36 closes, the (negative) chargingvoltage of timing condenser C i.e., the voltage at point 4lcan berepresented as a function of time by a straight line 42 (FIG. 14) if thestart of the exponential charging of a capacitor is consideredsubstantially linear. In the charging circuit of capacitor C, a Zenerdiode 47 accurately determines the charging voltage for such capacitorso that the potential difference thereacross varies in a manner closelycorresponding to the straight line 42.

Since the emitter voltage of transistor Ta is substantially the same asthe voltage V0,, developed by the network CI r,., CT 2 and applied toits base, the switch 40 can select either a voltage V 6, on terminal 401or a voltage V 0, on terminal 40b (see FIG. 14), both of which areanalogues of 0,, and, therefore, of roll amplitude; voltage V,0,, can beused when the ship is stationary and voltage V 6, can be used when theship is moving; since, as has been seen, the moving-craft damping effect[3,, exceeds the stationary-craft damping effect 01,, a lower analoguevalue can be used when the ship is moving. This voltage selection is notcritical, however, for if selector 40 is kept on contact 40b when theship is stationary, all

that will happen will be reduction correction, whereas if seleche onlytor 40 is on contact 40a when the ship is moving, error will be anovercorrection of low-amplitude rolling.

The relative magnitudes of V 0, V 0, and of VE are so adjusted that, asseen in FIG. 14, V 61, and V 6, are exactly equal to 2VE for the rollamplitudes on standstill and in motion respectively corresponding to themaximum damping effect a, or ,6, of the stabilizing tanks. Thus, thesloping line 50 in FIG. 14 represents the voltage drop across resistorsr; in the limiting case where V 0, or V 0 equals 2VE. Consequently, whenhalf the roll amplitude is greater than the damping angle, the voltage Vat point 40 is greater than 2VE and, since the condenser voltage VC iszero at point 41 when maximum list to port is reached, the voltage V atpoint 43 and therefore on the base 44 of transistor Tb is greater thanthe threshold voltage VE. Tank filling is therefore initiated at aninstant close to the time t,,(B), thus at the desired moment asexplained with reference to FIG. 12. If, however, half the rollamplitude is less than the clamping angle so that the amplitude-analoguevoltage V at point 40 attains, say, only a value V,, at the time t,,(B),the voltage V at junction 43 will have only the value indicated by thepoint 51, less than VE. Only when the voltage VC of capacitor C, hasreached the charging potential U,,,, as shown by a sloping line 52, willthe voltage VE be attained at point 43. Filling will therefore start ata time t,,,, subsequent to the time t,,(B), the separation between thesetwo instants increasing progressively with decreasing roll amplitude.

Just as the controllers C,,B and C,,T determine the startoffilling timesfor the tanks 2B, and 2T,, respectively, the comparison circuit CVdetermines start-of-emptying times by interrupting the energization ofthese controllers at a time when the ship is passing through its meanposition To this end, the analogue voltage V0,, developed at e (FIG. 13)and the analogue voltage V0 picked up by the slider 26 are fed to thebases of respective transistors T,, T which are connected as emitterfollowers, with their emitters interconnected by way of the winding ofpolarized relay 39; two symmetrical networks 55, which comprise Zenerand ordinary diodes and which shunt the winding of relay 39, limit thevoltages applied thereto and absorb switching transients.

When the analogue voltage of angle 9 in this balanced arrangement isgreater than the analogue voltage of angle 0 the armature 37 engages thecontact 38 The list is then to starboard in relation to the meanposition of the ship, and controller C,,T is energized via contacts Pand 36,. Controller C,,T is deenergizedi.e., the starboard tank startsto emptyas soon as the analogue voltage of 0 has decreased below itsstored mean-position value, thus when the base potential of transistor Thas dropped below the base potential of transistor T, and the currentflow through the winding of relay 39 is reversed so that armature 37engages the contact 38,.

The operation of the circuit arrangement shown in FIG. 13 will more bedescribed in further detail. When the ship reaches its maximum excursionto one side, e.g. to starboard, first the remote pendulum contact (21,)opens and then the proximal pendulum contact (21 closes. When contact21, opens, relay M releases with the result that, through the agency ofrelay K,,, capacitors C8,, CT, and H are charged to the requiredpotential. When contact 21 closes, relay M responds and, by attractingits armature 36 energizes the controller C,,T for utilization of thestarboard-side analogue voltage V0,,. During the immediately precedinghalf period the capacitor CT along with capacitor CB had been chargedand had retained its charge, the contacts m, and m then being open. Whencontact m closes immediately after the charging of capacitor CT,, thevoltage V0,, is transmitted to controller C,,T and the timet,(T) isregistered therein. A As has been seen, the time t,(T) cannot be delayedbeyond the passage of the ship through its mean position. Upon suchpassage the contact 38 opens and the contact P closes so that a pulsetraverses the relay N, which discharges the capacitors CT and C3,. Thestorage capacitors therefore retain their charge for about threequarter-cycles of an oscillation. In the interval between the opening ofone set of contacts and the closure of the other, these capacitors cancharge undisturbed to the potential representing the maximum relativeswing of the pendulum 18; their discharge occurs as soon as there iscertainty that the information stored in them has been used. Thisinterval is determined by the angular play between the unit 20 and thependulum 18. This play, by way of example, can be on the order of andcorresponds of course to the roll-amplitude threshold below which noantirolling action is initiated.

The refilling time t, is determined in either of the controllerswhenever a simultaneous closure of contacts P 36 or P 36,, indicatesthat the maximum roll excursion to one side is greater than the storedmean angle of heel (0, If this is exceptionally not the case, theantiroll system does not operate. The time t, corresponds to the startof filling of the tank on the corresponding side, such filling ceasingupon the start of emptying at the time t determined by the movement ofthe armature 37.

The oscillation period T may vary, e.g. because of ship loading or ofthe swell, but this does not impede the operation of the system. whichadapts itself to the new period, for the state of charge of the storagecondensers decreases substantially linearly in time so that the analogueof swing angle 0,, for each side varies with time as indicated by thesloping lines 60, 61, 62 in F IG. 14.

If S denotes the voltage threshold corresponding to the angular playbetween the reference unit 18 and the mobile unit 20, the longest periodT /4 for which the system can operate is determined by a sloping line 64and its horizontal extension 65 intersecting the charging curve 42. Ifthe period decreases to a value T T,,, the voltage given by theintersection of threshold line 60 with an ordinate V 6 corresponds tothe same minimum roll angle. However, an analogue voltage V,,, for agiven roll angle, represented by line 61, changes to a higher voltageV',, for the same angle upon a decrease of the period from T to T. Asshown by a sloping line 66, the startof-filling time advancesconcurrently from t to t',,,,. Thus, any reduction in the length of theoscillatory period is compensated by a more rapid response of the rollstabilizer.

The simplified system shown in FIG. 17 is designed for cases where it isnot necessary to determine the ships mean position between twoconsecutive extreme angles of heel, its stabilizer including but onepair of tanks operating only on heavy rolling. A relay winding M,associated with one of the two sides of the ship (its symmetricalcounterpart not being illustrated) is controlled as before by one of thecontacts (21,) of the rocking assembly 18, 20 and operates a reversingarmature 68 forming part of the controller for the particular sideconcerned; when in its solid-line position, armature 68 enables acapacitor 69 to be charged by a stabilized voltage V. The capacitorcircuit is closed via a tap on a voltage divider 71, 72. When contact 68is in its dotted line position, capacitor 69 discharges into a circuitcomprising, in parallel, a relay winding 73 and a resistance 74.

Via its armature 79 the relay winding controls, as in the precedingembodiment, the energization of the solenoid valve controlling tankfilling (or the operation of equivalent antiroll means) corresponding tothe particular side concerned; also, the relay 73, 79 is so designedthat a drop in the voltage across its winding 73i.e. across capacitor69below a critical value V (FIG. 18) releases the armature 79.

If the total resistance and therefore the time constant of the chargingcircuit of capacitor 69 is twice that of its discharging circuit, theslope 75a (FIG. 18) at the start of the charging curve for capacitor 69is half the absolute value of the opposite slope 76a of its dischargingcurve 76. Consequently, since each of the contacts 21,, 21 stays closedfor substantially the time T/2, charging stops after that time at thepoint 77 and discharging restores the voltage across the relay windingto the value V during the next time interval T/4, whereupon the voltageV is maintained across capacitor 69 by a diode in parallel therewith.Contact 79 is therefore kept closed for a time T/4 during eachoscillation period T, and when the reversing switch 68 next returns toits solid-line position in the following period, charging of thecapacitor 69 restarts from the potential level V Thus, the relay circuitof FIG. 17 including condenser 69 acts as a delay network translating aclosure of contact 21, during the interval 0 I/4 into a closure ofcontacts 79 in the interval T/2 3T/4. This delay of corrective action byabout half a cycle, measured from the timing signal given by the openingor closure of contacts 21,, 21 is the same as that between the chargingof the storage condensers in FIG. 13 and the utilization of the storedcharge by controllers C 8 and C T.

FIG. 19 relates to a case in which the stabilizing means is an aileronhaving either a variable inclination (e.g. pitch angle) I or a fixedinclination and a variable effective length L (FIG. 4) transverse to thecraft. The roll is represented as a damped sinusoidal line 78, theassumption being that the antiroll means becomes effective when theswing already has reached certain minimum amplitude. Theaileron-extension signal can be generated at times t,,(B) and t,,(T),under the control of the units 18 and 20, whereas the inclination I orthe effective length L can be under the control of the parameter V0,,representing the peak amplitude.

FIG. relates to the case of ailerons of invariable efficiency (constantinclination and effective length), the control parameter being the timet, for which the aileron is extended. With a system of the kind shown inFIG. 17, aileron-extension time t, can coincide with a quarter-cycle ofthe oscillation; alternatively, for still greater effectiveness, theaileron can be made operative at a variable starting time t, determinedby the respective controller C B or C T shown in FIG. 13. Maximumdamping prevails of course when the aileron is always extended for halfacycle, as in the case of FIG. 19.

If only very large rolls are to be damped, the control system can belimited to the relatively movable elements 18 and 20 determining, as theonly controlling parameters, the consecutive instants t,,(B), t,,(T)which are established by the alternate operation of the contacts 21, and21, and which mark the start and the end of successive half-periods.

The embodiments hereinbefore described can of course be modified, by thesubstitution of equivalent structure and circuitry, without departingfrom the spirit and scope of this invention.

We claim:

1. In a craft subject to rolling motion about a longitudinal axis andequipped with stabilizer means for counteracting such rolling motion,the combination therewith of:

a reference member aboard the craft in the form of a weighted rodsuspended from a mounting with a pivotal axis parallel to saidlongitudinal axis;

a coacting member mounted aboard the craft for lateral angularentrainment thereby, said coacting member having a pair of armsbracketing said rod;

cooperating circuit means on said members for generating timing signalsduring predetermined relative positions thereof coinciding with maximumlateral excursions of the craft with reference to said axis, saidcircuit means including a first set of normally open contacts on saidrod and on one of said arms and a second set of normally open contactson said rod and on the other of said arms, said sets of contacts beingalternately closable in symmetrical relative positions of said arms andsaid rod, said an'ns being provided with frictional bearing meanssupporting same for swinging movement about a line parallel to saidlongitudinal axis, the friction of said bearing means being low enoughto let either of said arms come to rest against said rod upon anincipient swing of the craft to a respective side whereby thecorresponding set of contacts remains closed for substantially half arolling cycle; and

actuating means connected to said circuit means for periodically makingsaid stabilizer means effective in response to said timing signals.

2. The combination defined in claim 1 wherein said actuating meanscomprises a delay network for translating closure of either of said setsof contacts into corrective actuation of said stabilizer meanssubstantially half a rolling cycle later.

3. The combination defined in claim 2 wherein said delay networkincludes first relay means connected to operate in response to closureof either of said sets of contacts, condenser means chargeable by saidfirst relay means in the operated condition thereof, and second relaymeans connected for operation by a discharge current from said condensermeans in the unoperated condition of said first relay means.

4. The combination defined in claim 3 wherein said delay network furtherincludes a charging circuit for said condenser means and a dischargecircuit for said condenser means said ca acitive means to saidcontroller means. v

6. T e combination defined m claim 5 wherein one of said members isprovided with a generator of'variable voltage depending upon the heelangle of the craft with reference to the vertical, said capacitive meansbeing connectable by said second relay means to said generator forvarying said stored charge in accordance with said variable voltage,said condenser means having a discharge circuit through said secondrelay means with a time constant which is short compared with a rollingcycle.

7. The combination defined in claim 6 wherein said capacitive meanscomprises two pairs of identical capacitors and said generator includestwo complementary voltage sources each connectable by said switch meansto a respective capacitor of each pair at the end of a respectivehalf-cycle, said controller means comprising two controllers foroperating respective sections of said stabilizer means to correctlisting to corresponding sides, each pair of capacitors being providedwith a bridging voltage divider having two normally disconnected halvesinterconnectable by said switch means for transmission to acorresponding controller of the mean of the charges stored.

8. The combination defined in claim 7, further comprising a comparisoncircuit connected to receive from said generator an analogue voltageproportional to the mean heel angle of the craft between successivelateral excursions, together with the output of one of said sources, andthird relay means responsive to said comparison circuit for transmittingan activating signal to either of said controllers in dependence uponthe relative magnitude of said output and said analogue voltage.

9. The combination defined in claim 8 wherein said sections of saidstabilizer means each comprise a main tank and an auxiliary tank, firstvalve means responsive to a corresponding controller for alternatelyfilling and draining said main tank during part of a rolling cycle, andsecond valve means responsive to said analogue voltage for filling saidauxiliary tank to an extent determined by said mean heel angle.

10. The combination defined in claim 8 wherein each of said controllersincludes a timing condenser chargeable at a controlled rate in thepresence of said activating signal and signaling means responsive to apredetermined relationship between the charge on said timing condenserand the mean charge of the associated pair of capacitors transmittedthereto by said switch means.

11. The combination defined in claim 10 wherein each controller furtherincludes switchover means for modifying the' magnitude of said meancharge prior to comparison with the charge on said timing condenser.

12. The combination defined in claim 7 wherein said complementaryvoltage sources comprise a pair of arcuate potentiometer tracks rigidwith the craft and a pair of contactors on said rod respectively slidingalong said tracks.

13. The combination defined in claim 1 wherein said actuating meansincludes at least one amplifier with a pair of transistors of oppositeconductivity types having emitters interconnected by a low-impedancecircuit and having collectors connected to points of fixed potentials.

1. In a craft subject to rolling motion about a longitudinal axis andequipped with stabilizer means for counteracting such rolling motion,the combination therewith of: a reference member aboard the craft in theform of a weighted rod suspended from a mounting with a pivotal axisparallel to said longitudinal axis; a coacting member mounted aboard thecraft for lateral angular entrainment thereby, said coacting memberhaving a pair of arms bracKeting said rod; cooperating circuit means onsaid members for generating timing signals during predetermined relativepositions thereof coinciding with maximum lateral excursions of thecraft with reference to said axis, said circuit means including a firstset of normally open contacts on said rod and on one of said arms and asecond set of normally open contacts on said rod and on the other ofsaid arms, said sets of contacts being alternately closable insymmetrical relative positions of said arms and said rod, said armsbeing provided with frictional bearing means supporting same forswinging movement about a line parallel to said longitudinal axis, thefriction of said bearing means being low enough to let either of saidarms come to rest against said rod upon an incipient swing of the craftto a respective side whereby the corresponding set of contacts remainsclosed for substantially half a rolling cycle; and actuating meansconnected to said circuit means for periodically making said stabilizermeans effective in response to said timing signals.
 2. The combinationdefined in claim 1 wherein said actuating means comprises a delaynetwork for translating closure of either of said sets of contacts intocorrective actuation of said stabilizer means substantially half arolling cycle later.
 3. The combination defined in claim 2 wherein saiddelay network includes first relay means connected to operate inresponse to closure of either of said sets of contacts, condenser meanschargeable by said first relay means in the operated condition thereof,and second relay means connected for operation by a discharge currentfrom said condenser means in the unoperated condition of said firstrelay means.
 4. The combination defined in claim 3 wherein said delaynetwork further includes a charging circuit for said condenser means anda discharge circuit for said condenser means through said second relaymeans, said charging circuit having a time constant substantially twicethat of said discharge circuit whereby said second relay means operatesfor substantially a quarter of a rolling cycle.
 5. The combinationdefined in claim 3 wherein said actuating means further comprisescapacitive means for storing a charge applied thereto by said secondrelay means upon operation of the latter, controller means for saidstabilizer means, and switch means controlled by said first relay meansupon reoperation thereof for applying the stored charge from saidcapacitive means to said controller means.
 6. The combination defined inclaim 5 wherein one of said members is provided with a generator ofvariable voltage depending upon the heel angle of the craft withreference to the vertical, said capacitive means being connectable bysaid second relay means to said generator for varying said stored chargein accordance with said variable voltage, said condenser means having adischarge circuit through said second relay means with a time constantwhich is short compared with a rolling cycle.
 7. The combination definedin claim 6 wherein said capacitive means comprises two pairs ofidentical capacitors and said generator includes two complementaryvoltage sources each connectable by said switch means to a respectivecapacitor of each pair at the end of a respective half-cycle, saidcontroller means comprising two controllers for operating respectivesections of said stabilizer means to correct listing to correspondingsides, each pair of capacitors being provided with a bridging voltagedivider having two normally disconnected halves interconnectable by saidswitch means for transmission to a corresponding controller of the meanof the charges stored.
 8. The combination defined in claim 7, furthercomprising a comparison circuit connected to receive from said generatoran analogue voltage proportional to the mean heel angle of the craftbetween successive lateral excursions, together with the output of oneof said sources, and third relay means responsive to said comparisoncircuiT for transmitting an activating signal to either of saidcontrollers in dependence upon the relative magnitude of said output andsaid analogue voltage.
 9. The combination defined in claim 8 whereinsaid sections of said stabilizer means each comprise a main tank and anauxiliary tank, first valve means responsive to a correspondingcontroller for alternately filling and draining said main tank duringpart of a rolling cycle, and second valve means responsive to saidanalogue voltage for filling said auxiliary tank to an extent determinedby said mean heel angle.
 10. The combination defined in claim 8 whereineach of said controllers includes a timing condenser chargeable at acontrolled rate in the presence of said activating signal and signalingmeans responsive to a predetermined relationship between the charge onsaid timing condenser and the mean charge of the associated pair ofcapacitors transmitted thereto by said switch means.
 11. The combinationdefined in claim 10 wherein each controller further includes switchovermeans for modifying the magnitude of said mean charge prior tocomparison with the charge on said timing condenser.
 12. The combinationdefined in claim 7 wherein said complementary voltage sources comprise apair of arcuate potentiometer tracks rigid with the craft and a pair ofcontactors on said rod respectively sliding along said tracks.
 13. Thecombination defined in claim 1 wherein said actuating means includes atleast one amplifier with a pair of transistors of opposite conductivitytypes having emitters interconnected by a low-impedance circuit andhaving collectors connected to points of fixed potentials.